US 20070123769 A1
An apparatus for determining intraocular pressure includes a transducer assembly containing an applanation tonometer for the determination of a cornea applanation pressure and an ultrasonic pachymeter to determine the thickness of the cornea at the site of applanation. The assembly has a tip end which includes an applanation surface and an ultrasonic coupler surface, and an end cap membrane holder is adapted to fit over the tip end of the transducer assembly and hold a thin film membrane stretched over the applanation and ultrasonic coupler surfaces. The transducer assembly also has a detector for detecting the presence or absence of the end cap membrane holder, the detector may generate a signal to disable movement of the transducer assembly if the end cap is not detected.
1. An apparatus for determining intraocular pressure comprising:
a transducer assembly containing an applanation tonometer for the determination of a cornea applanation pressure and an ultrasonic pachymeter to determine the thickness of the cornea at the site of applanation, the assembly having a tip end which includes an applanation surface and an ultrasonic coupler surface;
an end cap membrane holder adapted to fit over the tip end of the transducer assembly and hold a thin film membrane stretched over the applanation and ultrasonic coupler surfaces; and
a detector for detecting the presence or absence of the end cap membrane holder.
2. An apparatus as in
3. An apparatus as in
4. An apparatus as in
5. An apparatus as in
6. An apparatus as in
7. An apparatus as in
8. An apparatus as in
9. An apparatus as in
10. An apparatus as in
11. An apparatus as in
12. An apparatus as in
This application is a continuation in part of application Ser. No. 10/890,615 filed Jul. 14, 2004, and also claims priority for any new matter to provisional application 60/724,086 filed Oct. 6, 2005. This application further claims priority through the parent application Ser. No. 10/890,615 to a provisional patent application having Ser. No. 60/489,681, which was filed on Jul. 24, 2003.
The invention relates to the field of devices and methods for measuring intraocular pressure for diagnostic and treatment purposes; and to the specific field of devices and methods using ultrasonic pachymetery to calibrate applanation tonometry readings for variations in cornea thickness in order to yield more accurate measurement of intraocular pressure.
Glaucoma refers to a specific pattern of optic nerve damage and visual field loss caused by a number of different eye diseases. Frequently, these diseases are characterized by elevated intraocular pressure; a leading risk factor for development of glaucoma. Devices that measure intraocular pressure are referred to as tonometers.
A particular method of measuring intraocular pressure is known as applanation tonometery, a pressure measurement technique based on the principal that pressure inside a liquid filled sphere can be determined by measuring the force required to flatten a portion of the surface. Applanation tonometers measure either the degree of indentation of the cornea produced by an application probe, or they measure the force required for the probe to flatten a defined area of the cornea, and then translate the measurement into an indication of intraocular pressure. Applanation tonometery was popularized by Goldmann as an improved method of intraocular pressure determination in comparison to indentation tonometery or invasive intraocular pressure measurements. Goldmann applanation tonometery uses and indirect pressure measurement technique based on the Imbert-Fink principal which teaches that pressure inside a liquid filled sphere can be determined by measuring the force required to flatten a portion of the surface. There are several indirect measurement devices in addition to the Goldmann tonometer that have been conceived, e.g. the Mackey Marg, Perkins and Draeger to name a few. They measure either the degree of indentation of the cornea produced by an application probe or they measure the force required for the probe to flatten a defined area of the cornea. Details of such previous devices are widely available in numerous textbooks and will not be discussed herein.
It is known that variations in thickness of the cornea affect the accuracy of applanation pressure techniques. A thinner than normal cornea would flatten more readily than a normal thickness cornea, and generate a falsely low estimate of intraocular pressure. Conversely, a thicker than normal cornea would overestimate the true intraocular pressure.
Recently, studies of ocular hypertensive patients sponsored by the National Eye Institute (NEI) of the National Institutes of Health (NIH) have demonstrated that corneal thickness is the single most important predictor of glaucoma. Corneal thickness is inversely proportional to the risk of developing glaucomatous damage. That is to say, among ocular hypertensives, the thinner the cornea the greater the risk of glaucoma.
Variations in corneal thickness can be measured by optical or ultrasonic means called pachymeters. However, it is time-consuming and expensive to use a second instrument, e.g. an ultrasonic pachymeter, sequentially with the tonometer. Moreover, it is impossible to know if the portion of the cornea applanated for tonometery was the portion whose thickness was measured. Further, the determination of both applanation tonometery and corneal pachymetry requires solving an equation in order to calculate the true intraocular pressure. As a result, the correction of applanation tonometery for corneal thickness variables is generally not widely done except in academic or research circumstances.
During Goldmann applanation tonometery, a fluorescent dye is applied to the corneal surface to aid in the pressure measurement. In an upright patient, the operator looks through the ocular of a slit lamp microscope in order to obtain a clear view of the cornea through the applanation device. Under direct vision and control of the operator, the applanation element is momentarily pressed onto the cornea. The cornea flattens as a result of the force applied by the applanation element. This in turn causes a change in the pattern of fluorescence. The operator observes these changes and when the pattern of fluorescence reaches a predetermined endpoint the intraocular pressure is determined. This method also helps to reduce inadvertent trauma to the delicate epithelial layer of the cornea. This technique, as well as measurements with the classical tonometers, requires training, skill and experience because it is important not to under applanate or over applanate the cornea.
U.S. Pat. No. 6,083,161 and CIP Ser. No. 10/234,294, filed on Sep. 3, 2002, disclose a new apparatus and method which provides more accurate intraocular pressure determination. The apparatus measures conventional tonometery as well as corneal thickness using a single integrated device. Both measurements are made on the exact same region of the cornea. The apparatus uses a transparent corneal applanation element for the determination of the applanation pressure. An ultrasonic transducer is preferably coaxial with or part of the tonometer transducer and is used to measure corneal thickness. Such a design would normally partially skewer the view of the cornea and make the measurement difficult or impossible. However, the apparatus uses an internal reflection technique in order to view around the obscuration. This improved method still suffers, however, from the difficulty of measurement through use of fluorescent dye viewed through a generally non-mobile slit-lamp microscope with patients seated in an upright position. Further, it requires a well-trained and skilled operator in order to obtain accurate and repeatable results.
Hyman teaches a method for determining intraocular pressure using a conventional slit lamp-based Goldmann style tonometer and a pachymeter correcting for corneal thickness. After the pachymeter signal is generated, this method requires the application probe to be moved in a direction toward the subjects' eye until a measurement endpoint is observed by the observer. This method is cumbersome and costly. In addition, the method requires the application probe to be in contact with the cornea for a long time. Contact with the cornea for an extended period of time can alter the intraocular pressure and is uncomfortable for the patient.
There are instances where accurate IOP determination is required and where skilled operators are not present, e.g. examining patients during hospital rounds, emergency rooms, private ophthalmic and optometrist's offices, intern's offices, etc. Further, the use of a portable or handheld tonometer is beneficial or required when the patient is not in an upper right position, e.g. the operating room during surgery, use with children and infants and during patient rounds on the hospital floors. While there are some portable tonometers available, they cannot measure or correct for corneal thickness.
There exists a need, therefore, for a simple to use, portable device that does not require trained personnel to simultaneously perform tonometery and pachymetry, that registers more accurate intraocular pressure for general clinical use, and can be used in any patient position. The present invention applanates the cornea with an ultrasonic transducer while simultaneously recording applanation pressure and corneal thickness in the exact region of applanation. The present invention can be configured for use as either a fixed or mobile device and can be used in any position. A microprocessor converts the applanation pressure to an adjusted intraocular pressure, which more accurately reflects the true intraocular pressure when compared to conventional applanation tonometery. This device and method allows for quick, convenient, easy to use, portable and precise determination of intraocular pressure.
The device also may use a transparent membrane that covers the contact tip of the ocular probe, which provides a sterile barrier and prevents tear fluid from the eye from migrating into the probe. The membrane may be stretched over the contact tip by a membrane holder end cap holder cap. The device may have an end cap detection system and an interlock system to prevent the device from operation unless a protective membrane holder is in place.
The shape of the ultrasound transducer crystal may be flat, or more preferably have a curved concave surface that conforms to a convex surface of the acoustic coupler.
The structure of the force coupler between the applanation disc and the force sensor a may be a unitary coupling, or more preferably, a two-segment coupler wherein a small diameter sensor rod with a rounded tip passes through the ultrasonic transducer and contacts a larger surface of a transducer rod.
Other objects, purposes and aspects of this invention will become apparent upon review of the invention as described herein. However, the invention is not intended to be restricted in form nor limited in scope to the embodiments described, but rather is intended to include the full scope of the claims appended hereto.
It is a preferred embodiment of the present invention to obtain more accurate intraocular pressure measurements using a solid-state, ultrasonic cornea thickness measuring means working in the 10 to 20 MHz frequency domain in functional association with a pressure sensing means as an applanation surface of predetermined area for contact with the corneal surface.
In another preferred embodiment, the applanation surface is a replaceable membrane.
In another preferred embodiment, the pressure sensing means is located proximal to the applanation surface and in functional relation to the corneal surface.
In another preferred embodiment, the device displays a digital LED readout of the applanation pressure, the corneal thickness and the intraocular pressure adjusted for corneal thickness.
It is yet a further preferred embodiment in which the measurement system incorporates a sensing means responsive to proper positioning of the system.
A patient preparing for Laser Assisted In situ Keratomileusis (LASIK) photorefractive surgery for minus eight diopters (−8 D) of myopia has a preoperative central corneal thickness of 452 microns. Six months following the LASIK procedure the intraocular pressure is measured as determined by Goldmann tonometery as 16 mmHg. The uncorrected intraocular pressure as determined by the present invention is also 16 mmHg. Pachymetry indicates the central corneal thickness to be 347 microns. The corrected intraocular pressure as determined by the present invention is 25 mmHg. In this example the present invention demonstrated that the intraocular pressure was higher than would be otherwise apparent; potentially masking glaucoma. The normal intraocular pressure ranges from 12 to 21 mmHg.
A patient presented for a routine of found that examination has an intraocular pressure of 19 mmHg as determined by Goldmann tonometery. The uncorrected intraocular as determined by the present invention is also 19 mmHg. Pachymetry indicates the central corneal thickness to be 485 microns. The corrected intraocular pressure as determined by the present invention is 23 mmHg. In this example the present invention demonstrated that the intraocular pressure was higher than would be otherwise apparent; masking glaucoma.
The apparatus of this invention described and shown herein is a novel device for simultaneous measurement, at the same locus of applanation, pressure and surface thickness of a fluid filled sphere for more accurate determination of intracavity pressure, wherein at least a portion of the applanation surface is an ultrasonic transducer. The method for utilizing this device includes the simultaneous measurement, at the same locus of applanation, intracavity pressure and surface thickness of a fluid filled sphere for more accurate determination of intracavity pressure. In addition this novel device provides for simultaneous measurement, at the same locus of applanation, tonometery and pachymetry for determination of more accurate intraocular pressure, wherein at least a portion of the applanation surface is an ultrasonic transducer. Further, the method and device of the invention herein can provide for a fixation light source to stabilize the patient eye during applanation. Further yet, this invention includes a method of simultaneous measurement, at the same locus of applanation tonometery and pachymetry for the purpose of more accurate intraocular pressure determination. The locus of applanation tonometery and pachymetry is preferably the cornea of the eye.
Referring now to the drawings,
As illustrated in
As also shown in
As shown in
Alternatively, as shown in
Alternatively, as shown in
As shown earlier in
In the embodiment shown in
With the need to remove a contaminated membrane after each use, there is a substantial risk of forgetting to replace the membrane before the next use. Given the serious effect of an unprotect use on the delicate instrument, it would be highly beneficial to have some type of lockout protection that inhibits the device from operating unless a membrane is in place, and in a manner that prevents or warns against the movement of the probe toward contact with the patient's eye. Thus, as shown in shown in
Another advantage of this light transmitting membrane holder 642 is that it can be shaped as in
Variations or modifications to the subject matter of this invention may occur to those skilled in the art upon review of the summary provided herein, in addition to the description of its preferred embodiment, in light of the drawings. Such variations, if within the spirit of this invention, are intended to be encompassed within the scope of the invention as described herein.